Low pressure separator having an internal divider and uses therefor

ABSTRACT

Improvements in biological conversion processes and associated apparatuses are disclosed for the generation of useful end products such as ethanol, through metabolic pathways of C1-fixing bacteria that utilize, as a nutrient, a C1-carbon source from a C1-containing substrate such as an industrial waste gas. Particular aspects of the disclosure relate to the downstream recovery of ethanol and/or isopropanol from bleed and permeate streams and more particularly to performing such recovery with improved efficiency that can advantageously reduce capital (e.g., equipment) and/or operating (e.g., utility) costs. Particular aspects related to the downstream recovery of ethanol and/or isopropanol using a low pressure separator having an internal divider.

FIELD OF THE INVENTION

Aspects of the invention relate to the microbial fermentation of aC1-containing substrate to ethanol, utilizing a bioreactor system thatproduces a filtered permeate stream and bacteria-containing bleedstream. Aspects more specifically relate to processes for obtainingethanol from these streams in an efficient manner, particularly in termsof heat integration.

DESCRIPTION OF RELATED ART

Environmental concerns over fossil fuel greenhouse gas (GHG) emissionshave led to an increasing emphasis on renewable energy sources. As aresult, ethanol is rapidly becoming a major hydrogen-rich liquidtransport fuel around the world. Continued growth in the global marketfor the fuel ethanol industry is expected for the foreseeable future,based on increased emphasis on ethanol production in Europe, Japan, andthe United States, as well as several developing nations. For example,in the United States, ethanol is used to produce E10, a 10% mixture ofethanol in gasoline. In E10 blends, the ethanol component acts as anoxygenating agent, improving the efficiency of combustion and reducingthe production of air pollutants. In Brazil, ethanol satisfiesapproximately 30% of the transport fuel demand, as both an oxygenatingagent blended in gasoline, and as a pure fuel in its own right. Inaddition, the European Union (EU) has mandated targets, for each of itsmember nations, for the consumption of sustainable transport fuels suchas biomass-derived ethanol.

The vast majority of fuel ethanol is produced via traditionalyeast-based fermentation processes that use crop derived carbohydrates,such as sucrose extracted from sugarcane or starch extracted from graincrops, as the main carbon source. However, the cost of thesecarbohydrate feed stocks is influenced by their value in the marketplacefor competing uses, namely as food sources for both humans and animals.In addition, the cultivation of starch or sucrose-producing crops forethanol production is not economically sustainable in all geographies,as this is a function of both local land values and climate. For thesereasons, it is of particular interest to develop technologies to convertlower cost and/or more abundant carbon resources into fuel ethanol. Inthis regard, carbon monoxide (CO) is a major, energy-rich by-product ofthe incomplete combustion of organic materials such as coal, oil, andoil-derived products. CO-rich waste gases result from a variety ofindustrial processes. For example, the steel industry in Australia isreported to produce and release into the atmosphere over 500,000 metrictons of CO annually.

More recently, micro-organism (bacterial) based process alternatives forproducing ethanol from CO on an industrial scale have become a subjectof commercial interest and investment. The ability of micro-organismcultures to grow, with CO being the sole carbon source, was firstdiscovered in 1903. This characteristic was later determined to residein an organism's use of the acetyl coenzyme A (acetyl CoA) biochemicalpathway of autotrophic growth (also known as the Woods-Ljungdahl pathwayand the carbon monoxide dehydrogenase/acetyl CoA synthase (CODH/ACS)pathway). A large number of anaerobic organisms includingcarboxydotrophic, photosynthetic, methanogenic, and acetogenic organismshave since been shown to metabolize CO. Anaerobic bacteria, such asthose from the genus Clostridium, are known to produce ethanol from CO,CO₂ and H₂ via the acetyl CoA biochemical pathway. For example, variousstrains of Clostridium ljungdahlii that produce ethanol from gases aredescribed in WO 00/68407; EP 1117309 A1; U.S. Pat. No. 5,173,429; U.S.Pat. No. 5,593,886; U.S. Pat. No. 6,368,819; WO 98/00558; and WO02/08438. The bacterium Clostridium autoethanogenum sp is also known toproduce ethanol from gases (Abrini et al., ARCHIVES OF MICROBIOLOGY 161:345-351 (1994)).

Because each enzyme of an organism promotes its designated biologicalconversion with essentially perfect selectivity, microbial synthesisroutes can achieve higher yields with lower energy costs compared toconventional catalytic routes. In addition, concerns over the poisoningof catalysts, due to impurities in the reaction medium, are diminished.Despite these apparent advantages associated with the microbialsynthesis of ethanol from CO, such processes must nonetheless becompetitive with other technologies, in terms of ensuring that theproduction rate is competitive. When using CO as their carbon source,the anaerobic bacteria described above produce ethanol by fermentation,but they also produce at least one metabolite, for example CO₂, methane,n-butanol, and/or acetic acid. The formation of any of these metaboliteshas the potential to significantly impact productivity and overalleconomic viability of a given process, as available carbon is lost tothe metabolite(s) and the production efficiency of the desired endproduct is compromised. In addition, unless a metabolite (e.g., aceticacid) itself has value at the time and place of the microbialfermentation process, it may pose a waste disposal problem. Variousproposals for addressing the formation of products other than thedesired end product in the anaerobic fermentation of CO-containing gasesto make ethanol are discussed in WO2007/117157, WO2008/115080 andWO2009/022925.

Ethanol production rate, which is a key determinant as to whether agiven fermentation process is economically attractive, is highlydependent on managing the appropriate conditions for bacterial growth.For example, it is known from WO2010/093262 that the CO-containingsubstrate must be provided to a microbial culture at a rate that resultsin optimal microbial growth and/or desired metabolite production. Ifinsufficient substrate is provided, microbial growth slows and thefermentation product yields shift toward acetic acid at the expense ofethanol. If excessive substrate is provided, poor microbial growthand/or cell death can result. Further information regarding therelationships among operating parameters in these processes is found inWO2011/002318.

The art of biological processes for producing ethanol from CO, andparticularly CO-containing waste streams such as the gaseous effluentsemitted in steel production, is continually seeking solutions thatimprove process economics and therefore industry competitiveness. Onearea of interest relates to the energy requirements for separatingbyproducts, namely the metabolites described above that result fromnon-selective side reactions, as well as components of the bacterialculture medium (especially water), from the desired ethanol product. Forexample, achieving even modest advances in heat integration associatedwith the required separations downstream of the bioreactor(s),particularly if capital and operating expenses are not substantiallyimpacted, can have significant implications on the industrial scale ofoperation.

SUMMARY OF THE INVENTION

Aspects of the invention relate to improvements in biological conversionprocesses and associated apparatus for the generation of useful endproducts, through metabolic pathways of bacterium that utilize, as anutrient, carbon from a carbon containing substrate. Representativeprocesses comprise feeding a substrate to a bioreactor system comprisingat least a first bioreactor including a culture medium and a bacteriumto metabolize a carbon source in the substrate and produce at least onefermentation product; withdrawing from the bioreactor system a bleedstream comprising bacterium; withdrawing from the bioreactor system apermeate stream obtained from filtration of a liquid product of thebioreactor system; and feeding at least a portion of the bleed streamand at least a portion of the permeate stream to a low pressureseparator comprising a divider. The divider being configured to isolate,in a lower section, a liquid fraction of the bleed stream from a liquidfraction of the permeate stream, and also configured to combine, in anupper section, a gaseous fraction of the bleed stream with a gaseousfraction of the permeate stream.

According to further aspects, the invention relates to improvements inbiological conversion processes and associated apparatuses for thegeneration of useful end products such as ethanol and/or isopropanol,through metabolic pathways of C1-fixing bacteria that utilize, as anutrient, C1 gases from a C1 containing substrate such as an industrialwaste gas. Representative processes and apparatuses involve alternativetypes of operation that are particularly advantageous in conjunctionwith high ethanol or isopropanol productivities. The associated,substantial product flow rates must be processed in an efficient mannerthrough the separation unit operations needed to achieve a high purityend product (e.g., anhydrous ethanol or isopropanol). An exemplarybioreactor system that may be used for achieving desirable ethanol orisopropanol productivity (e.g., expressed in terms of grams per day perliter of bioreactor volume) may comprise two or more bioreactorsoperating in series with respect to the flow of liquid inputs andoutputs.

That is, according to such a system, a feed stream of liquid culturemedium may be passed to a first bioreactor, and one or more liquidscomprising contents of this bioreactor (having the same or differentcompositions relative to the bulk, first bioreactor liquid) may bepassed to a second bioreactor, with one or more liquids comprisingcontents of the second bioreactor (having the same or differentcompositions relative to the bulk, second bioreactor liquid) beingprocessed through separation unit operations to purify the ethanol orisopropanol contained in these liquids. This advantageously allows forthe separate control of conditions in separate bioreactors for differingobjectives (e.g., bacterial growth vs. product yield), leading toenhancements in ethanol productivity and/or reductions in byproductproductivity, relative to the use of a single reactor with comparableoverall volume. If a bioreactor system includes more than twobioreactors, then intermediate liquid products may be fed to, andwithdrawn from, intermediate bioreactors in series (i.e., passed tosuccessively downstream bioreactors). The terms “subsequent” or“downstream,” when referring to a bioreactor, refer to its position withrespect to other bioreactors of a bioreactor system, in terms of thepassage of reactor liquids (e.g., culture medium) from one bioreactor tothe next. Representative bioreactor systems comprising two or morebioreactors may also operate in parallel with respect to the flow ofgaseous feeds and products, such that a gaseous C1-containing substratemay be divided and fed at the same or differing flow rates to thebioreactors simultaneously (e.g., by introducing the substrate to gasdistributors in their lower sections). Gaseous products, depleted in C1gas composition relative to the substrate, may be withdrawn separatelyfrom each of the bioreactors simultaneously and then further processed,for example to recover entrained liquid product, as separate streams oras a combined stream.

Whilst the description that follows pertains to ethanol fermentations,it is considered that the teachings are equally applicable toisopropanol fermentation processes and isopropanol purificationprocesses. Furthermore, whilst the embodiments provided relate to gasfermentation processes, it is considered that the invention would beapplicable to any fermentation process generating a fermentation brothcontaining excreted liquid products and biomass.

During normal operation of a bioreactor system, the net generation ofliquid products requires that these products be withdrawn, preferably ona continuous basis, to prevent their accumulation in each bioreactor andthereby maintain steady-state conditions. If all of the withdrawn liquidhas the same, bulk composition as that existing in the bioreactor(including the same concentrations of bacteria and culture mediumcomponents), then the bioreactor, although operating at steady-statewith respect to ethanol and acetic acid concentration, would becomesteadily depleted in bacteria concentration. Under such circumstances, agreater productivity of ethanol relative to the productivity (growth) ofbacteria would result directionally in a faster rate of bacteriadepletion from a given bioreactor. In order to maintain bacteriaconcentration by providing an additional operating degree of freedom, afirst part of the liquid withdrawn from a given bioreactor, i.e., ableed stream, may be an unfiltered part, whereas a second part of theliquid withdrawn may be filtered. In this case, the first part may havesubstantially the same, bulk composition as that existing in thebioreactor, or at least substantially the same bacteria concentration,whereas the second part of the liquid, by virtue of filtration, may bedivided into a filtration retentate that is enriched in bacteria andreturned to bioreactor to maintain its bacteria concentration, and afiltration permeate that represents the net fraction of the withdrawn,second part that is actually removed from the bioreactor (or notrecycled to the bioreactor). This filtration permeate, substantiallyfree of bacteria, may then be passed to a downstream bioreactor, or, inthe case of its removal from the final bioreactor, may be processedthrough separation unit operations to purify the ethanol containedtherein.

In this manner, the withdrawal of both bleed and permeate streamsprovides for a significantly improved degree of overall process control,especially in terms of managing the bacteria concentration in abioreactor at varying levels of productivity. As the rate of ethanolgeneration increases, the flow of the permeate stream relative to theflow of the bleed stream can be increased, allowing more filteredreactor liquid to be withdrawn with greater retention of bacteria.Because ethanol is present in both of these withdrawn streams, the bleedand permeate streams that are ultimately withdrawn from a bioreactorsystem, for example from a final stage bioreactor (such as from a secondbioreactor of a bioreactor system comprising first and secondbioreactors operating in series with respect to liquid flow), arenormally both further processed for ethanol purification. The bleed andpermeate streams are sent to individual storage tanks, with effluentsfrom these tanks then sent to downstream recovery units.

In view of this, aspects of the present invention relate to thedownstream recovery of ethanol or isopropanol from bleed and permeatestreams and more particularly to performing such recovery with improvedefficiency that can advantageously reduce capital (e.g., equipment)and/or operating (e.g., utility) costs. More specific aspects relate toprocesses and associated apparatuses for the purification of ethanol orisopropanol contained in both bleed and permeate streams, withdrawn frombioreactor processes, based on differences in relative volatilitybetween ethanol (normal boiling point=78° C.) and other components inthese streams, including water (normal boiling point=100° C.), as wellas metabolites such as acetic acid (normal boiling point=118° C.),2,3-butanediol (normal boiling point=177° C.), and various other simpleorganic alcohols and acids. Exemplary processes and apparatuses utilizeat least a single stage of vapor-liquid equilibrium to achieve thedesired enrichment of ethanol or isopropanol in a vapor or overheadfraction of a separator, which separates this fraction from a liquid orbottoms fraction. The term “separator” therefore encompasses asingle-stage flash drum. Preferably, however, a representative separatorwill utilize multiple stages of vapor-liquid equilibrium, as in the caseof a distillation column, in order to achieve higher purity of theethanol or isopropanol product in the overhead. The term “separator”also encompasses such single-stage or multi-stage vessels having anauxiliary flow of gas (e.g., a stripper) and/or an auxiliary flow orliquid (e.g., a scrubber) to enhance a desired component separation.

Regardless of the type of separator, however, an input of heat isusually necessary to carry out such separation processes, and, moreparticularly, a consumption of heat at a relatively high temperature inat least one stage, such as a reboiler stage, which may be accompaniedby a recovery of heat at a relatively low temperature in another stage,such as a condenser stage. In this regard, further aspects of thepresent invention more particularly relate to the discovery of processesand apparatuses with which heat integration is improved in the recoveryof ethanol or isopropanol from bleed and permeate streams that arewithdrawn from bioreactor systems. Such recovery is complicated by thefact that the former stream contains some of the bacteria used in thebiological conversion process, whereas the latter stream is normallyfree or at least substantially free of such bacteria. The presence ofbacteria in the bleed stream, for example, places constraints on theoperating temperatures used in a distillation column or other separatorused to purify this stream, while the same considerations do not applyin processing the permeate stream.

According to one aspect of the present invention, an opportunity toimprove heat integration in the face of differing bleed stream andpermeate stream flow rates arises in processing at least part, andoptionally all, of the permeate stream together with the bleed stream ina single separator. A divider in the separator for co-processing bleedand permeate streams can advantageously isolate the respective liquidfractions of these streams, having different compositions due to atleast the presence of bacteria in the former and absence of bacteria inthe latter. This beneficially allows these liquid fractions to bewithdrawn in separate liquid bottoms streams that are used for separatepurposes, such as the removal of bacteria in the case of a bleed streambottoms and/or recycle back to the bioreactor system in the case of apermeate stream bottoms. Alternatively, a permeate stream bottoms can beprocessed according to objectives associated with wastewater treatment,such as the reduction of chemical oxygen demand (COD). Whether a portionof, or all of, the permeate stream is fed to the separator forco-processing bleed and permeate streams, the divider may be offset orpositioned off-center, such that the liquid volumes that are isolated inthe separator for the bleed stream bottoms and permeate stream bottomsare unequal. For example, the liquid volume isolated for the former maybe smaller than the liquid volume isolated for the latter, particularlyin the case of processes operating with relatively high net ethanolproductivities, such as at least 55 grams/day, per liter of bioreactorvolume, requiring relatively high permeate stream flow rates.

The divider may extend to an axial height that is less than the axialheight of the separator itself, such that gaseous fractions of the bleedand permeate streams, in contrast to the liquid fractions of thesestreams, are allowed to combine. The energy input to a single separator(e.g., including energy to one or more reboilers of a low pressuredistillation column, used to heat one or both of the liquid fractions)can therefore be efficiently utilized to obtain a separator overheadenriched in ethanol or isopropanol and obtained from both the bleedstream and the permeate stream, or otherwise portions of one or both ofthese streams, simultaneously. In this regard, aspects of the inventionexploit the particular characteristics of the bleed and permeate streamsin the recovery of ethanol or isopropanol, namely their differingcompositions in terms of non-volatile components (and particularly thebacteria concentration) but similar, or identical, compositions in termsof proportions of volatile components (and particularly ethanol orisopropanol, water, and acetic acid concentrations on a bacteria-freebasis). Such characteristics are used as a basis for obtaining efficientheat integration and other advantages, including reduced equipmentcapacity and/or cost, according to processes and associated apparatusesdescribed herein.

These and other embodiments, aspects, and advantages relating to thepresent invention are apparent from the following Detailed Description.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the exemplary embodiments of thepresent invention and the advantages thereof may be acquired byreferring to the following description in consideration of theaccompanying figures, in which the same or similar features areidentified by the same or similar reference numbers.

FIG. 1 depicts a representative bioreactor system utilizing twobioreactors, which provide a bleed stream and a permeate stream asdescribed herein.

FIG. 2 depicts a process according to the illustrated, representativeschematic flow diagram and associated equipment, for recovering ethanolusing a low pressure separator comprising a divider.

FIG. 3. depicts a process according to the illustrated, representativeschematic flow diagram and associated equipment, for recovering ethanolfrom a bioreactor system as shown in FIG. 1, and particularly from thebleed stream and permeate stream withdrawn from this system.

FIGS. 1 to 3 should be understood to present an illustration of thedisclosure and/or principles involved. In order to facilitateexplanation and understanding, simplified process flow schemes andequipment are depicted, and these figures are not necessarily drawn toscale. Details including valves, instrumentation, and other equipmentnot essential to the understanding of the disclosure are not shown. TheFigures are directed to processes for ethanol production and recovery,however, it is considered that the disclosure and principles involvedare equally applicable to isopropanol production. As is readily apparentto one of skill in the art having knowledge of the present disclosure,processes for recovering ethanol from streams produced in bioreactorsystems in an equipment cost-efficient manner and/or a utilitycost-efficient manner, according to other embodiments of the invention,will have configurations determined, in part, by their specific use.

DETAILED DESCRIPTION

Exemplary embodiments of the invention are directed to biologicalconversion process comprising feeding a substrate to a bioreactor systemcomprising at least a first bioreactor including a culture medium and abacterium to metabolize a carbon source in the substrate and produce atleast one fermentation product. The processes further compriseswithdrawing from the bioreactor system a bleed stream comprisingC1-fixing bacteria, and also withdrawing from the bioreactor system apermeate stream obtained from filtration of a liquid product of thebioreactor system. The processes further comprise feeding the bleedstream and the permeate stream to a low pressure separator comprising adivider configured to isolate (e.g., separate, in a liquid tightmanner), in a lower section, a liquid fraction of the bleed stream froma liquid fraction of the permeate stream. For example, the liquidfraction of the bleed stream may provide a first liquid volume in fluidcommunication with the bleed stream and the liquid fraction of thepermeate stream may provide a second liquid volume in fluidcommunication with the permeate stream. The divider may also beconfigured to combine, in an upper section, a gaseous fraction of thebleed stream with a gaseous fraction of the permeate stream. Forexample, a combined gaseous fraction of the bleed stream and permeatestream may provide a gaseous volume in fluid communication with a lowpressure separator overhead.

In particular embodiments of the invention, the process furthercomprises partitioning the permeate stream into at least a firstpermeate portion and a second permeate portion and feeding the firstpermeate portion to a high pressure separator (e.g. high pressuredistillation column) and feeding the second permeate portion to a lowpressure separator (e.g. low pressure distillation column.

In particular embodiments of the invention, the biological conversionprocesses comprises feeding a gaseous C1-containing substrate to abioreactor system comprising at least (i) a first bioreactor including aculture medium and C1-fixing bacteria (cells or biomass), which may becontained in the first bioreactor, and optionally (ii) a second oradditional downstream bioreactors, with the bioreactors being utilizedto metabolize a C1 component in the C1-containing substrate and therebyproduce ethanol. In embodiments involving the use of both a highpressure separator (e.g., high pressure distillation column) forpurifying ethanol from a first permeate portion and a low pressureseparator (e.g., low pressure distillation column) for purifying ethanolfrom a second permeate portion, in conjunction with purifying ethanolfrom at least a portion of the bleed stream, heat integration mayinclude utilizing heat generated in one of the separators forconsumption in the other separator. Advantageously, a condensertemperature of the high pressure separator may exceed a reboilertemperature of the low pressure separator, such that at least a portionof the high pressure separator condenser heat may be consumed asreboiler heat in the low pressure separator reboiler, or otherwise in atleast one low pressure separator reboiler (e.g., a low pressureseparator bleed reboiler used to vaporize at least a portion of a lowpressure separator bleed liquid outlet stream and/or a low pressureseparator permeate reboiler used to vaporize at least a portion of a lowpressure separator permeate liquid outlet stream) if more than onereboiler are used. In some embodiments, for example embodiments that donot involve partitioning a permeate stream, the process does not includean additional separator for fractionating a portion of the permeatestream. Therefore, for example, the entire permeate stream may be fed toa separator comprising a divider as described above. More particularly,the permeate and bleed streams may be fed to opposite sides of thedivider, positioned within a separator that is used to co-process thesestreams.

Yet other embodiments of the invention are directed to biologicalconversion apparatuses comprising a bioreactor system comprising (i) aninlet (e.g., in fluid communication with at least one, at least two,and/or all bioreactors of the bioreactor system) for introducing asubstrate to the bioreactor system, (ii) at least a first bioreactor forcontaining a culture medium and bacteria to metabolize a carboncomponent in the substrate and produce a desired end product, (iii) afiltration system for filtering a liquid product of the bioreactorsystem, (iv) a bleed stream outlet (e.g., in fluid communication with atleast one bioreactor of the bioreactor system) for withdrawing a bleedstream comprising bacteria, and (v) a permeate stream outlet in fluidcommunication with a permeate side of the filtration system forwithdrawing a permeate stream from the bioreactor system. Theapparatuses may optionally comprise a recycle conduit in fluidcommunication with a retentate side of the filtration system formaintaining a recycle portion of bacteria in the bioreactor system. Inparticular aspects, the biological conversion apparatus comprises abioreactor system comprising (i) an inlet for introducing aC1-containing substrate, to the bioreactor system, (ii) at least a firstbioreactor for containing a culture medium and C1-fixing bacteria tometabolize a C1 component in the C1-containing substrate and produce atleast one product selected from the group consisting of ethanol,isopropanol and mixtures thereof.

Representative apparatuses further comprise a low pressure separatorhaving a divider disposed in a lower section thereof and configured forisolating (i) a first liquid volume in fluid communication with both (A)the bleed stream outlet, at a low pressure separator bleed stream inletpositioned in the lower section and (B) a low pressure separator bleedliquid outlet positioned below the low pressure bleed stream inlet from(ii) a second liquid volume in fluid communication with both (A) thepermeate stream outlet, at a low pressure separator permeate streaminlet positioned in the lower section and (B) a low pressure separatorpermeate liquid outlet positioned below the low pressure separatorpermeate stream inlet.

According to certain embodiments, the low pressure separator may beconfigured for combining, in an upper section thereof (e.g., a sectionresiding above the divider, or residing at an axial height that isgreater than that to which the divider extends), a first gaseousfraction above the first liquid volume with a second gaseous fractionabove the second liquid volume and to provide a combined gaseous volumein fluid communication with a low pressure separator vapor outlet, forexample at the upper section, such as at or near the top of the lowpressure separator. The low pressure separator may be configured with alow pressure separator condenser in fluid communication with the lowpressure separator vapor outlet and both (i) a low pressure separatoroverhead reflux conduit and (ii) a low pressure separator overheadconduit. The low pressure separator may also be configured with a lowpressure separator bleed reboiler in fluid communication with the lowpressure separator bleed liquid outlet and both (i) a low pressureseparator bleed liquid reflux conduit and (ii) a low pressure separatorbleed bottoms conduit. The low pressure separator may further beconfigured with a low pressure separator permeate reboiler in fluidcommunication with the low pressure separator permeate liquid outlet andboth (i) a low pressure separator permeate liquid reflux conduit and(ii) a low pressure separator permeate bottoms conduit. In lieu of beingconfigured with both a low pressure separator bleed reboiler and a lowpressure separator permeate reboiler, the low pressure separator mayalternatively be configured with a low pressure separator reboiler influid communication with both the low pressure separator bleed liquidoutlet and the low pressure separator permeate liquid outlet, inaddition to the low pressure separator bleed liquid reflux conduit andlow pressure separator permeate liquid flux conduit, as well as the lowpressure separator bleed bottoms conduit and low pressure separatorpermeate bottoms conduit.

Representative apparatuses may optionally further comprise a highpressure separator having (i) a first permeate portion inlet in fluidcommunication with the permeate stream outlet, for receiving a firstpermeate portion of the permeate stream and passing a second permeateportion of the permeate stream to the low pressure separator permeatestream inlet, (ii) a high pressure separator vapor outlet (for example,in the upper section, such as at or near the top of the high pressureseparator), and (iii) a high pressure separator liquid outlet (forexample, in the lower section, such as at or near the bottom). The firstpermeate portion inlet is normally positioned below the high pressureseparator overhead outlet and above the high pressure separator bottomsoutlet. The high pressure separator may be configured with a highpressure separator condenser in fluid communication with the highpressure separator vapor outlet and both (i) a high pressure separatoroverhead reflux conduit and (ii) a high pressure separator overheadconduit. The high pressure separator may also be configured with a highpressure separator reboiler in fluid communication with the highpressure separator liquid outlet and both (i) a high pressure separatorliquid reflux conduit and (ii) a high pressure separator bottomsconduit. Any of, or any combination of, the low pressure separatorcondenser, the low pressure separator bleed reboiler, the low pressureseparator permeate reboiler, and the low pressure separator reboiler, asdescribed above, may be configured to provide heat integration with thehigh pressure separator condenser and/or the high pressure separatorreboiler, as described above. According to exemplary embodiments, thehigh pressure separator condenser may be configured to transfer heatgenerated in this condenser, to be consumed in the low pressureseparator bleed reboiler and/or the low pressure separator permeatereboiler, or the low pressure separator reboiler, as described above.

Representative apparatuses may optionally also comprise a dehydrationcolumn having (i) a dehydration column inlet in fluid communication withboth the low pressure separator overhead outlet and the high pressureseparator overhead outlet, (ii) a dehydration column overhead outlet(for example, in the upper section, such as at or near the top), and(iii) a dehydration column bottoms outlet (for example, in the lowersection, such as at or near the bottom). The dehydration column inlet isnormally positioned below the dehydration column overhead outlet andabove the dehydration column bottoms outlet. Representative apparatusesmay optionally additionally comprise a second filtration system in fluidcommunication with the low pressure separator bleed bottoms outlet, forfiltering a low pressure separator bleed bottoms stream, for example toseparate C1-fixing bacteria contained in this stream.

In view of the above, particular aspects of the invention are directedto biological conversion processes and associated apparatuses, in whicha C1-containing substrate is fed to a bioreactor system comprising atleast one bioreactor, for the production of a fermentation product thatis recovered from the bioreactor system in liquid permeate and bleedstreams. In particular aspects, the fermentation product is selectedfrom the group consisting of ethanol (C₂H₅OH) and isopropanol (C₃H₇OH).Bioreactor systems comprising multiple (e.g., two or more, such as two,three, or four) bioreactors can advantageously allow for the separatecontrol of conditions in each bioreactor to accomplish differentprocessing objectives. For example, in the case of a bioreactor systemcomprising two bioreactors, a first bioreactor may be operated primarilyfor growth of the bacterial culture that is supplied continuously orintermittently to a second bioreactor. The second bioreactor, in turn,may be operated primarily for the generation of ethanol, i.e., themaximization of ethanol or isopropanol product yield.

The use of such bioreactor systems, with a parallel flow of theC1-containing substrate to the bioreactors and series flow of liquidproducts from a first bioreactor to subsequent bioreactor(s), asdescribed above, is associated with high fermentation productconcentrations in liquid bleed stream(s) and liquid permeate stream(s)that are withdrawn from the bioreactor system, as described herein.Often, all or substantially all of the ethanol produced in a biologicalconversion process is recovered from bleed and permeate streamswithdrawn from a final bioreactor, which is namely the most downstreambioreactor of the bioreactor system (e.g., in the case of the finalbioreactor being a second bioreactor, positioned downstream of a firstbioreactor, in a bioreactor system having two and only two bioreactors).It is also possible, however, for at least a portion of the ethanolproduced to be recovered from a bleed stream and/or a permeate streamwithdrawn from the first bioreactor and/or any intermediate bioreactors(upstream of the final bioreactor) of a bioreactor system. Inrepresentative embodiments, the C1 containing substrate is a gaseoussubstrate comprising CO. In representative embodiments, any such bleedand/or permeate stream(s), for example withdrawn from a finalbioreactor, may have an ethanol concentration of generally at leastabout 40 grams per liter (grams/liter or g/L) (e.g., from about 40 toabout 95 g/L), typically at least about 50 g/L (e.g., from about 50 toabout 80 g/L), and often at least about 60 g/L (e.g., from about 60 toabout 75 g/L). Any such bleed and/or permeate stream(s), for examplewithdrawn from a final bioreactor, may have a weight ratio of ethanol toacetic acid of generally at least about 5:1 (e.g., from about 5:1 toabout 100:1), typically at least about 7.5:1 (e.g., from about 7.5:1 toabout 50:1), and often at least about 10:1 (e.g., from about 10:1 toabout 50:1). In general, the analytical methods (e.g., gaschromatography (GC) or high pressure liquid chromatography, HPLC) usedto determine concentrations of ethanol and other metabolites requirecell-free samples, and therefore may require an initial separation(e.g., membrane filtration) to be performed on the bleed stream toremove C1-fixing bacteria (cells or biomass). Accordingly,concentrations of ethanol and other metabolites, as well as otherproperties of bleed streams as described herein (e.g., theethanol:acetic acid weight ratio) are expressed on a biomass-free basis.

The present invention therefore generally relates to processes forproducing a desired end product, such as ethanol or isopropanol, byfeeding C1-carbon source in a gaseous C1-containing substrate to abioreactor system comprising one or more bioreactors. In operation, theone or more bioreactors comprise a liquid culture medium containingC1-fixing bacteria. In addition to the desired end product, processes asdescribed herein additionally generate undesired or less desiredmetabolites. Examples of metabolites that may be generated in additionto a desired fermentation product, are acetate (e.g., in the form ofacetic acid), 2,3-butanediol, and lactate (e.g., in the form of lacticacid). Gaseous CO₂ may also be generated.

Representative bacteria or microbes of the invention may be or may bederived from a C1-fixing microorganism, an anaerobe, an acetogen, anethanologen, a carboxydotroph, and/or a methanotroph. Table 1 provides arepresentative list of microorganisms and identifies their functionalcharacteristics.

TABLE 1 C1-fixing Anaerobe Acetogen Ethanologen Autotroph CarboxydotrophMethanotroph Acetobacterium woodii + + + +/−¹ − − − Alkalibaculumbacchii + + + + + + − Blautia producta + + + − + + − Butyribacteriummethylotrophicum + + + + + + − Clostridium aceticum + + + − + + −Clostridium autoethanogenum + + + + + + − Clostridiumcarboxidivorans + + + + + + − Clostridium coskatii + + + + + + −Clostridium drakei + + + − + + − Clostridium formicoaceticum + + + − + +− Clostridium ljungdahlii + + + + + + − Clostridium magnum + + + − ++/−² − Clostridium ragsdalei + + + + + + − Clostridiumscatologenes + + + − + + − Eubacterium limosum + + + − + + − Moorellathermautotrophica + + + + + + − Moorella thermoacetica (formerly + + +−³ + + − Clostridium thermoaceticum) Oxobacter pfennigii + + + − + + −Sporomusa ovata + + + − + +/−⁴ − Sporomusa silvacetica + + + − + +/−⁵ −Sporomusa sphaeroides + + + − + +/−⁶ − Thermoanaerobacter kiuvi + + +− + − − ¹ Acetobacterium woodi can produce ethanol from fructose, butnot from gas. ²It has not been investigated whether Clostridium magnumcan grow on CO. ³One strain of Moorella thermoacetica, Moorella sp.HUC22-1, has been reported to produce ethanol from gas. ⁴It has not beeninvestigated whether Sporomusa ovata can grow on CO. ⁵It has not beeninvestigated whether Sporomusa silvacetica can grow on CO. ⁶It has notbeen investigated whether Sporomusa sphaeroides can grow on CO.

“C1” refers to a one-carbon molecule, for example, CO, CO₂, CH₄, orCH₃OH. “C1-oxygenate” refers to a one-carbon molecule that alsocomprises at least one oxygen atom, for example, CO, CO₂, or CH₃OH.“C1-carbon source” refers a one carbon-molecule that serves as a partialor sole carbon source for the microorganism of the invention. Forexample, a C1-carbon source may comprise one or more of CO, CO₂, CH₄,CH₃OH, or CH₂O₂. Preferably, the C1-carbon source comprises one or bothof CO and CO₂. A “C1-fixing microorganism” is a microorganism that hasthe ability to produce one or more products from a C1-carbon source.Typically, the microorganism of the invention is a C1-fixing bacterium.In a preferred embodiment, the microorganism of the invention is derivedfrom a C1-fixing microorganism identified in Table 1.

An “ethanologen” is a microorganism that produces or is capable ofproducing ethanol. Typically, the microorganism of the invention is anethanologen. In a preferred embodiment, the microorganism of theinvention is derived from an ethanologen identified in Table 1.

An “autotroph” is a microorganism capable of growing in the absence oforganic carbon. Instead, autotrophs use inorganic carbon sources, suchas CO and/or CO₂. Typically, the microorganism of the invention is anautotroph. In a preferred embodiment, the microorganism of the inventionis derived from an autotroph identified in Table 1.

A “carboxydotroph” is a microorganism capable of utilizing CO as a solesource of carbon. Typically, the microorganism of the invention is acarboxydotroph. In a preferred embodiment, the microorganism of theinvention is derived from a carboxydotroph identified in Table 1.

A “methanotroph” is a microorganism capable of utilizing methane as asole source of carbon and energy. In certain embodiments, themicroorganism of the invention is derived from a methanotroph.

More broadly, the microorganism of the invention may be derived from anygenus or species identified in Table 1.

In a preferred embodiment, the microorganism of the invention is derivedfrom the cluster of Clostridia comprising the species Clostridiumautoethanogenum, Clostridium ljungdahlii, and Clostridium ragsdalei.These species were first reported and characterized by Abrini, ArchMicrobiol, 161: 345-351, 1994 (Clostridium autoethanogenum), Tanner, IntJ System Bacteriol, 43: 232-236, 1993 (Clostridium ljungdahlii), andHuhnke, WO 2008/028055 (Clostridium ragsdalei).

These three species have many similarities. In particular, these speciesare all C1-fixing, anaerobic, acetogenic, ethanologenic, andcarboxydotrophic members of the genus Clostridium. These species havesimilar genotypes and phenotypes and modes of energy conservation andfermentative metabolism. Moreover, these species are clustered inclostridial rRNA homology group I with 16S rRNA DNA that is more than99% identical, have a DNA G+C content of about 22-30 mol %, aregram-positive, have similar morphology and size (logarithmic growingcells between 0.5-0.7×3-5 μm), are mesophilic (grow optimally at 30-37°C.), have similar pH ranges of about 4-7.5 (with an optimal pH of about5.5-6), lack cytochromes, and conserve energy via an Rnf complex. Also,reduction of carboxylic acids into their corresponding alcohols has beenshown in these species (Perez, Biotechnol Bioeng, 110:1066-1077, 2012).Importantly, these species also all show strong autotrophic growth onCO-containing gases, produce ethanol and acetate (or acetic acid) asmain fermentation products, and produce small amounts of 2,3-butanedioland lactic acid under certain conditions.

However, these three species also have a number of differences. Thesespecies were isolated from different sources: Clostridiumautoethanogenum from rabbit gut, Clostridium ljungdahlii from chickenyard waste, and Clostridium ragsdalei from freshwater sediment. Thesespecies differ in utilization of various sugars (e.g., rhamnose,arabinose), acids (e.g., gluconate, citrate), amino acids (e.g.,arginine, histidine), and other substrates (e.g., betaine, butanol).Moreover, these species differ in auxotrophy to certain vitamins (e.g.,thiamine, biotin). These species have differences in nucleic and aminoacid sequences of Wood-Ljungdahl pathway genes and proteins, althoughthe general organization and number of these genes and proteins has beenfound to be the same in all species (Köpke, Curr Opin Biotechnol, 22:320-325, 2011).

Thus, in summary, many of the characteristics of Clostridiumautoethanogenum, Clostridium ljungdahlii, or Clostridium ragsdalei arenot specific to that species, but are rather general characteristics forthis cluster of C1-fixing, anaerobic, acetogenic, ethanologenic, andcarboxydotrophic members of the genus Clostridium. However, since thesespecies are, in fact, distinct, the genetic modification or manipulationof one of these species may not have an identical effect in another ofthese species. For instance, differences in growth, performance, orproduct production may be observed.

The microorganism of the invention may also be derived from an isolateor mutant of Clostridium autoethanogenum, Clostridium ljungdahlii, orClostridium ragsdalei. Isolates and mutants of Clostridiumautoethanogenum include JA1-1 (DSM10061) (Abrini, Arch Microbiol, 161:345-351, 1994), LBS1560 (DSM19630) (WO 2009/064200), and LZ1561(DSM23693). Isolates and mutants of Clostridium ljungdahlii include ATCC49587 (Tanner, Int J Syst Bacteriol, 43: 232-236, 1993), PETCT(DSM13528, ATCC 55383), ERI-2 (ATCC 55380) (U.S. Pat. No. 5,593,886),C-01 (ATCC 55988) (U.S. Pat. No. 6,368,819), O-52 (ATCC 55989) (U.S.Pat. No. 6,368,819), and OTA-1 (Tirado-Acevedo, Production of bioethanolfrom synthesis gas using Clostridium ljungdahlii, PhD thesis, NorthCarolina State University, 2010). Isolates and mutants of Clostridiumragsdalei include PI 1 (ATCC BAA-622, ATCC PTA-7826) (WO 2008/028055).

“Substrate” refers to a carbon and/or energy source for themicroorganism of the invention. Typically, the substrate is gaseous andcomprises a C1-carbon source, for example, CO, CO₂, and/or CH₄.Preferably, the substrate comprises a C1-carbon source of CO or CO+CO₂.The substrate may further comprise other non-carbon components, such asH₂, N₂, or electrons.

The substrate generally comprises at least some amount of CO, such asabout 1, 2, 5, 10, 20, 30, 40, 50, 60, 70, 80, 90, or 100 mol % CO. Thesubstrate may comprise a range of CO, such as about 5-70, 20-80, 30-70,or 40-60 mol % CO. Preferably, the substrate comprises about 40-70 mol %CO (e.g., steel mill or blast furnace gas), about 20-30 mol % CO (e.g.,basic oxygen furnace gas), or about 15-45 mol % CO (e.g., syngas). Insome embodiments, the substrate may comprise a relatively low amount ofCO, such as about 1-10 or 1-20 mol % CO. The microorganism of theinvention typically converts at least a portion of the CO in thesubstrate to a product. In some embodiments, the substrate comprises noor substantially no (<1 mol %) CO.

The substrate may comprise some amount of H₂. For example, the substratemay comprise about 1, 2, 5, 10, 15, 20, or 30 mol % H₂. In someembodiments, the substrate may comprise a relatively high amount of H₂,such as about 60, 70, 80, or 90 mol % H₂. In further embodiments, thesubstrate comprises no or substantially no (<1 mol %) H₂.

The substrate may comprise some amount of CO₂. For example, thesubstrate may comprise about 1-80 or 1-30 mol % CO₂. In someembodiments, the substrate may comprise less than about 20, 15, 10, or 5mol % CO₂. In another embodiment, the substrate comprises no orsubstantially no (<1 mol %) CO₂.

Although the substrate is typically gaseous, the substrate may also beprovided in alternative forms. For example, the substrate may bedissolved in a liquid saturated with a CO-containing gas using amicrobubble dispersion generator. By way of further example, thesubstrate may be adsorbed onto a solid support.

The substrate and/or C1-carbon source may be a waste gas obtained as abyproduct of an industrial process or from some other source, such asfrom automobile exhaust fumes or biomass gasification. In certainembodiments, the industrial process is selected from the groupconsisting of ferrous metal products manufacturing, such as a steel millmanufacturing, non-ferrous products manufacturing, petroleum refiningprocesses, coal gasification, electric power production, carbon blackproduction, ammonia production, methanol production, and cokemanufacturing. In these embodiments, the substrate and/or C1-carbonsource may be captured from the industrial process before it is emittedinto the atmosphere, using any convenient method.

The substrate and/or C1-carbon source may be syngas, such as syngasobtained by gasification of coal or refinery residues, gasification ofbiomass or lignocellulosic material, or reforming of natural gas. Inanother embodiment, the syngas may be obtained from the gasification ofmunicipal solid waste or industrial solid waste.

The composition of the substrate may have a significant impact on theefficiency and/or cost of the reaction. For example, the presence ofoxygen (O₂) may reduce the efficiency of an anaerobic fermentationprocess. Depending on the composition of the substrate, it may bedesirable to treat, scrub, or filter the substrate to remove anyundesired contaminants, such as toxins (for example, HCN, acetylene),undesired components, or dust particles, and/or increase theconcentration of desirable components. For example, the gaseousC1-containing substrate may be filtered (contacted with a solid medium,such as activated carbon) or scrubbed (contacted with a liquid medium,such as an aqueous solution of an acid, a base, an oxidizing agent, or areducing agent) using known methods, or otherwise may be subjected toadsorption to remove preferentially adsorbed contaminants. Pressureswing adsorption (PSA) and/or temperature swing adsorption (TSA), inparticular, may be used to remove contaminants that are detrimental tothe functioning of the carboxydotrophic bacteria, such as hydrogencyanide (HCN) and aromatic compounds including benzene, toluene, and/orxylenes (BTX). The substrate preferably does not include contaminants,to the extent that such contaminants might have an adverse effect on thegrowth of the carboxydotrophic bacteria (e.g., one or morecontaminant(s) are not present in concentrations or amounts such thatthe growth rate is reduced by more than 10% under a given set ofconditions, compared to the growth rate under the same conditions, butwithout the contaminant(s)

Whilst representative embodiments of the invention disclose the use ofC1-carbon sources, and C1-fixing bacterium, it is considered thataspects of the invention apply to any biological conversion processwhereby both a permeate stream and a bleed stream are withdrawn from abioreactor.

Broader aspects of the invention are intended to capture non-gaseousfermentation processes, as well as microorganisms and feedstocksapplicable to the fermentation process.

In particular aspects, the non-gaseous substrate is a carbohydratesubstrate, and the bacterium is a bacterium capable of fixing a carbonsubstrate in the carbohydrate substrate. Processes for the conversion ofcarbohydrate substrates to products, including ethanol, are known.Carbohydrate feedstocks may include sugars (for example glucose,sucrose, fructose, xylose, arabinose and glycerol) cellulose, andbiomass (for example, corn starch, sugarcane, crop residues such as cornstover and sugarcane bagasse, purpose-grown grass crops, and woody plantbiomass.

In particular aspects, the microorganism applicable to the fermentationprocess is selected from the group consisting of yeast, fungus, algae,cyanobacteria or bacteria. Exemplary bacterium, applicable to thefermentation process, include Escherichia coli, Klebsiella oxytoca,Bacillus subtilus, Zymomonas mobilis, Lacotococcus lactis, andClostridium acetobutylicum. Exemplary yeasts of fungi include speciesfrom the genus Saccharomyces, Candida, Lipomyces, Rhodosporidium,Rhodotorula, and Yarrowia.

In the context of an acidic metabolite that is acetic acid, the terms“acetic acid” or “acetate” refer to the total acetate present in theculture medium, either in its anionic (dissociated) form (i.e., asacetate ion or CH₃COO⁻) or in the form of free, molecular acetic acid(CH₃COOH), with the ratio these forms being dependent upon the pH of thesystem. The terms “lactic acid” and “lactate” are used analogously, torefer to the total lactate present in the culture medium. As describedbelow, a basic neutralizing agent such as aqueous sodium hydroxide(NaOH) may be used to control the pH of the culture medium in a givenbioreactor (e.g., to a pH value that may be between pH=4.0 and pH=8.0),for example by neutralizing acetic acid and optionally other minoracidic components. Representative pH ranges at which bioreactors aremaintained for carrying out the processes described herein are fromabout 4.5 to about 7.0, such as from about 4.5 to about 6.5.

A specific type of bioreactor that is particularly useful in thepractice of the present invention is a circulated loop reactor thatrelies on a density gradient between a relatively low density sectionwithin a riser and a relatively high density section within one or more,internal or external downcomers. Both the riser and downcomer sectionsinclude liquid culture medium in a continuous liquid phase zone, but thegaseous C1-containing substrate is normally distributed (e.g., sparged)into the bottom of the riser section only. Rising gas bubbles areconfined to this section during their upward movement through thecontinuous liquid phase zone, until any unconsumed and undissolved gasis released into a continuous gas phase zone (i.e., vapor space orheadspace) above the liquid level. The downward liquid circulation,through either an internal or external liquid downcomer, may be inducedor aided by an optional loop pump.

The term “bioreactor,” as well as any bioreactor that may be included aspart of a “bioreactor system,” is not limited to a circulated loopreactor, but more broadly includes any suitable vessel, or sectionwithin a vessel, for maintaining a liquid volume of culture medium withC1-fixing bacteria that may be used to carry out the biologicalprocesses described herein, which may also be referred to asfermentation processes to the extent that they are generally conductedanaerobically. Particular types of bioreactors can include any vesselssuitable for two-phase (gas-liquid) contacting, for examplecounter-current flow reactors (e.g., with an upwardly-flowing vaporphase and downwardly-flowing liquid phase) or co-current flow reactors(e.g., with upwardly-flowing gas and liquid phases). In such two-phasecontacting vessels, it is possible for the liquid phase to be thecontinuous phase, as in the case of gas bubbles flowing through a movingcolumn of liquid. Otherwise, it is possible for the vapor phase to bethe continuous phase, as in the case of a dispersed liquid (e.g., in theform of droplets) flowing through a vapor space. In some embodiments,different zones of a bioreactor may be used to contain a continuousliquid phase and a continuous gas phase.

Specific examples of bioreactors include Continuous Stirred TankReactors (CSTRs), Immobilized Cell Reactors (ICRs), Trickle Bed Reactors(TBRs), Moving Bed Biofilm Reactor (MBBRs), Bubble Columns, Gas LiftFermenters, and Membrane Reactors such as Hollow Fiber MembraneBioreactors (HFMBRs). Suitable bioreactors may include static mixers, orother vessels and/or devices (e.g., towers or piping arrangements),suitable for contacting the gaseous C1-containing substrate with aculture medium and particularly the C-fixing bacteria contained therein(e.g., with dissolution and mass transport kinetics favorable forcarrying out the biological conversion process). A bioreactor system maycomprise two or more bioreactors of different types, although generallyall bioreactors in a bioreactor system are of one type (e.g., circulatedloop reactors).

Some suitable process streams, operating parameters, and equipment foruse in the biological processes described herein are described in U.S.patent application Publication No. US2011/0212433, which is herebyincorporated by reference in its entirety. One or more bioreactors, forexample all bioreactors, of bioreactor systems described herein may havea superatmospheric pressure, for example generally in the range fromabout 50 kPag (in which the notation “kPag” is meant to indicate unitsof kPa gauge pressure) to about 1,000 kPag and often in the range fromabout 200 kPa to about 800 kPag. One or more bioreactors, and preferablyall bioreactors, of bioreactor systems described herein have afermentation broth temperature that is suitable for vitality and growthof the C1-fixing bacteria. Representative temperatures are in a rangefrom about 25° C. to about 45° C., and more typically from about 30° C.to about 40° C.

Bioreactor systems with multiple bioreactors operating in series withrespect to the flow of liquid inputs and outputs and also operating inparallel with respect to the flow of gaseous feeds and products, asdescribed herein, can provide favorable overall C1 utilization. Theoverall C1 utilization refers to the percentage of C1 that is input tothe bioreactor system (e.g., the total C1-carbon source in theC1-containing substrate that is fed to the bioreactors) and utilized inthe conversion to fermentation products(s) (e.g., ethanol orisopropanol) and other metabolites of the bacteria. If the combinedcomposition of the gaseous product withdrawn from the bioreactor system(i.e., the combined gas outlet stream(s) withdrawn from thebioreactor(s)) is known or can be calculated (e.g., based on the flowrates and compositions of the gas outlet stream(s)), then the overall COutilization may be calculated as:

1−(rate of CO withdrawn from the system)/(rate of CO fed to the system).

The overall CO utilization is determined on a “per pass” or“once-through” basis, without accounting for the use of gaseous productrecycle (and added expense) that can provide higher total utilizationvalues. According to representative embodiments, the CO utilization bythe C1-fixing bacteria is generally at least about 35% (e.g., from about35% to about 85%), typically at least about 50% (e.g., from about 50% toabout 80%), and often at least about 60% (e.g., from about 60% to about75%). In some cases, CO utilization may be at least about 70%.

FIG. 1 depicts a representative bioreactor system 100 comprising a firstbioreactor 10 and a second bioreactor 20. As shown, CO-containingsubstrate 12 to bioreactor system 100 is divided into separate, firstbioreactor gas inlet stream 14 and second bioreactor gas inlet stream14′, which are fed, respectively, to first and second bioreactors 10, 20through their respective gas inlets 16, 16′, positioned near the bottomsof bioreactors 10, 20. Gas inlet streams 14, 14′ may be fed throughrespective gas distributors, such as spargers, positioned at gas inlets16, 16′ and configured to produce fine bubbles (not shown) ofCO-containing substrate in respective continuous liquid phase zones 18,18′ of bioreactors 10, 20 and thereby improve gas-liquid mass transfer.

As described above, the bacteria concentration in continuous liquidphase zones 18, 18′ of bioreactors 10, 20 can be maintained at varyinglevels of ethanol productivity (corresponding to varying liquid productwithdrawal rates) by providing a means whereby filtered and unfilteredparts of liquid may be withdrawn. In the embodiment depicted in FIG. 1,first bioreactor filtration system 25, in communication with continuousliquid phase zone 18, allows for the withdrawal of intermediate permeatestream 28, which is filtered and substantially free of C1-fixingbacteria. First bioreactor retentate stream 36 allows for the return offiltered bacteria to first bioreactor 10. Liquid products withdrawn fromfirst bioreactor 10 may therefore comprise both intermediate permeatestream 28 and intermediate bleed stream 26, which is unfiltered andcontains C1-fixing bacteria (biomass) in substantially the sameconcentration as in the fermentation broth in continuous liquid phasezone 18 of first bioreactor 10. The relative amounts of the intermediateliquid product 32 withdrawn from first bioreactor 10 as intermediatebleed stream 26 and intermediate permeate stream 28 can be controlled tomeet the objectives of maintaining a desired biomass concentration and adesired rate of product (e.g., ethanol or isopropanol) removal. In thesame manner, second bioreactor filtration system 25′, in communicationwith continuous liquid phase zone 18′, allows for the withdrawal ofbleed stream 40 and permeate stream 50 from a final bioreactor ofbioreactor system 100, with the return of second bioreactor retentatestream 36′ to continuous liquid phase zone 18′ of second bioreactor 20.

Liquid culture medium may be fed, through culture medium inlet 34 tobioreactor system 100, and in particular to first bioreactor 10, tosupply nutrients for maintaining bacterial growth and to replace theliquid volume lost in intermediate liquid product 32 withdrawn fromfirst bioreactor 10, all or a portion of which may be passed to secondbioreactor 20. Optionally, liquid culture medium may likewise be fed tobioreactor system 100 through separate culture medium inlet 34′ tosecond bioreactor 20. Optionally, portions of intermediate bleed stream26 and/or intermediate permeate stream 28 may be withdrawn frombioreactor system 100 (e.g., for process monitoring and analysis),without passing to second bioreactor 20.

Gas outlet streams 38, 38′ may be withdrawn from conduits in fluidcommunication with respective continuous gas phase zones 22, 22′,constituting bioreactor headspace volumes above continuous liquid phasezones 18, 18′ comprising the culture medium and C1-fixing bacteria(i.e., comprising fermentation broth), through which the C1-containingsubstrate passes as a dispersed gas phase. Gas outlet streams 38, 38′may be withdrawn separately from bioreactor system 100 or, asillustrated in the embodiment of FIG. 1, combined and then withdrawn asgaseous product outlet 24. Gas outlet streams, or otherwise gaseousproduct outlet 24, may comprise one or more of, for example all of, (i)unreacted C1-components that passes through the fermentation brothwithout being metabolized (i.e., without being consumed in thebiological conversion process), (ii) components of the C1-containingsubstrate that are substantially not involved in (i.e., substantiallyinert to) the biological conversion process (e.g., N₂), (iii) CO₂produced as a metabolite of the biological conversion process, (iv)water vapor from the aqueous culture medium, and (v) various componentsof the C1-containing substrate that are present in minor or traceamounts (e.g., H₂, H₂S, NH₃, HCN).

Accordingly, FIG. 1 depicts a bioreactor system 100 in which gaseousC1-containing substrate 12 can be fed in parallel to first and secondbioreactors 10, 20, whereas liquid products, which can include C1-fixingbacteria (biomass), can be fed successively from first bioreactor 10 tosecond bioreactor 20. In the embodiment of FIG. 1, the final bioreactor,from which bleed stream 40 and permeate stream 50 are withdrawn frombioreactor system 100, is namely second bioreactor 20. In alternativeembodiments having bioreactor systems with additional bioreactors (e.g.,three or four bioreactors), and specifically one or more intermediatebioreactors downstream of a first bioreactor and upstream of a finalbioreactor, the gaseous and liquid feeds may be introduced to suchintermediate bioreactors in a similar manner, and the gaseous and liquidproducts may be withdrawn from such intermediate bioreactors in asimilar manner. Intermediate liquid products, including intermediatebleed and permeate streams, may be passed to and from successiveintermediate bioreactors in a similar manner. In general, one or moremetabolite products (e.g., ethanol) of bioreactor system 100 isrecovered from bleed and permeate streams, or portions thereof,withdrawn from a final bioreactor, such as bleed stream 40 and permeatestream 50 withdrawn from second bioreactor 20 in the embodiment ofFIG. 1. Optionally, such metabolite products may also be recovered frombleed and/or permeate streams, or portions thereof, withdrawn from oneor more bioreactors other than a final bioreactor.

FIG. 1 therefore schematically illustrates various feed streams that areinput to, and product streams that are withdrawn from, a representativebioreactor system. Embodiments of the invention can include otherfeatures not shown in FIG. 1, such as the use of (i) additives,including a basic neutralizing agent (e.g., NH₄OH or NaOH) and/or ananti-foaming agent; (ii) control systems (e.g., feedback control loops)and associated equipment, instrumentation, and software, for the controlof operating parameters (e.g., pH, temperature, and/or liquid level ofthe fermentation broth); (iii) external bioreactor recycle loops toimprove interphase mass transfer; (iv) internal bioreactor structures inthe continuous liquid phase zones (e.g., horizontal plates and/orpacking materials) and/or in the continuous vapor phase zones (e.g.,liquid distributors such as shower heads) to improve interphase masstransfer; (v) on-line sampling systems for continuous process monitoringand/or automated control; and/or (vi) recycle of liquid product(s),withdrawn from a bioreactor, to an upstream bioreactor

The recovery of metabolite products such as ethanol, according toembodiments of the invention, is described in greater detail withreference to FIG. 2. As shown, all or a portion of permeate stream 50,withdrawn from bioreactor system 100 (FIG. 1) and obtained fromfiltration of a liquid product of this system, is fed to a low pressureseparator 70, comprising a divider 80.

Unlike permeate stream 50, bleed stream 40 comprises C1-fixing bacteria(biomass), and, by virtue of the successive passage of liquid productsfrom upstream to downstream bioreactors, at least a portion, or all, ofthe biomass in bleed stream 40 may be biomass originally contained inthe first bioreactor (e.g., bioreactor 10 of FIG. 1). In general, bleedstream 40 may be any liquid product withdrawn from bioreactor system 100comprising fermentation broth (e.g., as an unfiltered liquid product),including biomass, whereas permeate stream 50 may be any liquid productwithdrawn from bioreactor system 100 comprising a filtered liquidproduct that is substantially free of biomass. Preferably, bleed stream40 and permeate stream 50 are both liquid products obtained from asubsequent bioreactor (e.g., second bioreactor 20 of bioreactor system100), disposed downstream of a first bioreactor, for example withrespect to the liquid product flows from one bioreactor to the next.Bleed stream 40 and permeate stream 50 may be unfiltered and filteredliquid products, respectively, obtained from directly from bioreactorsystem 100, or otherwise unfiltered and filtered products following (i)separation (e.g., other than filtration to remove biomass), for exampleinto streams of the same or different compositions and/or (ii) mixing(e.g., with other process streams or discreet additives).

Because of the presence of biomass, separation processes performed onbleed stream 40, unlike those performed on permeate stream 50, areadvantageously carried out at relatively lower temperatures to reducefouling of separation equipment. Consequently, a maximum temperature oflow pressure separator 70, to which bleed stream 40 is fed, is less thana maximum temperature of high pressure separator 60, to which permeatestream 50 is fed, in the absence of bleed stream 40. According to anembodiment, a maximum temperature of a low pressure separator, to whichbleed stream 40 is fed, is from about 55° C. to about 95° C., forexample from about 60° C. to about 80° C. According to the same or analternative embodiment, a maximum temperature of a high pressureseparator 60 is from about 95° C. to about 125° C. or from about 100° C.to about 120° C. In general, a temperature of at least one materialstream associated with high pressure separator 60 may exceed atemperature of at least one material stream associated with low pressureseparator 70, such that heat may be transferred from the former to thelatter. According to a particular embodiment, a minimum temperature ofhigh pressure separator 60, for example the temperature of high pressureseparator condenser 75, may exceed a maximum temperature of low pressureseparator 70 for example the temperature of low pressure separator bleedreboiler 45 and/or low pressure separator permeate reboiler 55, orotherwise simply the low pressure separator reboiler, for example if asingle reboiler is used for partial vaporization of both the lowpressure separator bleed outlet stream 71 and low pressure separatorpermeate outlet stream 77.

Because the bleed and permeate streams 40, 50 otherwise include waterand the same metabolite product(s) to be recovered, and considering thedifferences described above with respect to the operating temperaturesof the high and low pressure separators 60, 70, the use of separationsbased on differences in relative volatility require relatively lowerabsolute pressures to perform such separations on the bleed stream,compared to the pressures used with respect to the permeate stream.According to an embodiment, low pressure separator 70 has an absolutepressure that is nearly atmospheric pressure, for example from about 50kPa to about 150 kPa absolute pressure or from about 50 kPa to about 100kPa absolute pressure. According to the same or an alternativeembodiment, high pressure separator 60 may have an absolute pressurethat is greater than that of low pressure separator, but lower than apressure at which a final bioreactor operates. For example, highpressure separator may have a pressure from about 150 kPa to about 650kPa absolute pressure or from about 150 kPa to about 500 kPa absolutepressure. Alternatively, low pressure separator 70 may have vacuumpressure, i.e., an absolute pressure that is below atmospheric pressure,for example from about 20 kPa to about 90 kPa absolute pressure or fromabout 30 kPa to about 90 kPa absolute pressure.

According to the embodiment of FIG. 2, bleed stream 40, or at least aportion thereof, is fed, together with permeate stream 50 to lowpressure separator 70 (e.g., a low pressure, combined permeate and bleeddistillation column). Low pressure separator overhead 62 is withdrawn(e.g., as a vapor fraction) and, as described above, is enriched inethanol, relative to both bleed stream 40 and permeate stream 50. Due tothe presence of divider 80 in low pressure separator 70, bleed stream 40and permeate stream 50 can be co-processed in low pressure separator 70,in a manner whereby liquid levels can be isolated in a lower section,whereas gaseous fractions that are volatilized from these liquid levels(i.e., the liquid levels being namely liquid fractions of the bleedstream and second permeate portion, remaining after volatilization ofrespective gaseous fractions) can be combined in an upper section. Inthis manner, low pressure separator overhead 62 comprises ethanolseparated from both bleed stream 40 and permeate stream 50.

More specifically, divider 80 is configured to isolate (e.g., separate,in a liquid-tight manner), in a lower section A of low pressureseparator 70, liquid fraction 82 of bleed stream 40 from liquid fraction84 of permeate stream 50. Divider 80 is likewise configured to provide,in an upper section B of low pressure separator 70, combined gaseousfraction 86 of bleed stream 40 and permeate stream 50. Accordingly,liquid fraction 82 of bleed stream 40 provides a first liquid volume influid communication with bleed stream 40 and liquid fraction 84 ofpermeate stream 50 provides a second liquid volume in fluidcommunication with permeate stream 50. According to specificembodiments, the first volume may be smaller than or greater than thesecond volume, and the unequal volumes may be accommodated at leastpartly with divider 80 being positioned in a non-central location withinlow pressure separator 70 (e.g., being positioned in a manner whereby acentral vertical axis of the low pressure separator is offset from thedivider, such that they do not intersect). According to particularembodiments in which high productivities of metabolite products leaddirectionally to increased flow rates of the permeate stream relative tothe bleed stream, the first volume may be smaller than the second volumeand the divider may be offset from the central vertical axis, in adirection biased toward the location at which bleed stream 40 enters lowpressure separator 70.

According to one embodiment, divider 80 is in the form of a verticallyoriented plate, extending to a height in low pressure separator 70 thatis less than its axial height (e.g., less than 50%, or less than 30%, ofthe axial height of low pressure separator 70). However, regardless ofthe specific structure of divider 80, combined gaseous fraction 86 ofbleed stream 40 and permeate stream 50 can provide a gaseous volume influid communication with low pressure separator overhead 62. Also,according to the embodiment of FIG. 2, both a low pressure separatorbleed bottoms 64 and a low pressure separator permeate bottoms 66 may bewithdrawn from low pressure separator 70. In view of the abovedescription, low pressure separator bleed bottoms 64 may comprise, orconsist essentially of, liquid fraction 82 of bleed stream 40 and lowpressure separator permeate bottoms 66 may comprise, or consistessentially of, liquid fraction 84 of permeate stream 50 Liquid fraction82 of bleed stream 40 may therefore provide a first liquid volume, asdescribed above, that is in fluid communication with bleed stream 40 aswell as low pressure separator bleed bottoms 64, and/or liquid fraction84 of permeate stream 50 may provide a second liquid volume, asdescribed above, in fluid communication with permeate stream 50 as wellas low pressure separator permeate bottoms 66.

Advantageously, co-processing permeate stream 50 with at least a portionof bleed stream 40, also withdrawn from bioreactor system 100 (FIG. 1),improves overall process heat integration. According to a particularembodiment, the heat integration is based on relating, or adjusting, theflow rate of permeate stream 50 to the low pressure separator 70 atleast in part based on the flow rate of bleed stream 40 to thisseparator. For example, an increase in the flow rate of bleed stream 40may be accompanied by an increase in the flow rate of permeate stream50, with optionally the control of the flow rate of permeate stream 50being based on a measurement of the flow rate of bleed stream 40.Alternatively, the heat integration may account for the relativelygreater contribution of the permeate stream flow rate to the combinedbleed stream and permeate stream flow rates, at higher productivities ofmetabolite products (e.g., ethanol).

In a further embodiment, as depicted in FIG. 3. all or a portion of thepermeate stream 50 is partitioned into at least a first permeate portion50′ and a second permeate portion 50″. Second permeate portion 50″ isfed to a low pressure separator 70, along with bleed 40, as described inregards to FIG. 2 above. First permeate portion 50′ is fed to a highpressure separator 60. The partitioning of the permeate stream thereforerefers to dividing this stream into at least two portions, and oftenonly two portions. “Partitioning” does not preclude the use of optionalsteps, before and/or after dividing the permeate stream, which steps mayor may not affect the composition of the permeate stream and/or itsseparated portions. Such optional steps include for example (i)separating one or more additional portions (e.g., a third portion) fromthe permeate stream and/or its separated portions (e.g., for samplingpurposes), and/or (ii) mixing the permeate stream and/or its separatedportions with other streams and/or discreet additives (e.g., surfactantsor neutralizing agents, such as NH₄OH or NaOH). In some embodiments,however, a permeate stream withdrawn from a bioreactor system may bepartitioned into its separated portions that are fed to the high and lowpressure separators, without any of the permeate stream or its portionsundergoing (i) and/or (ii) above.

The relative flow rates of first permeate portion 50′ to high pressureseparator 60 and second permeate portion 50″ to low pressure separator70 may be based on, or adjusted according to, the total flow rate ofpermeate stream 50 in relation to the combined flow rate of bleed stream40 and permeate stream 50. For example, an increase in the total flowrate of permeate stream 50 in relation to the combined flow rate ofbleed stream 40 and permeate stream 50 may be accompanied by an increasein the flow rate of first permeate portion 50′, relative to secondpermeate portion 50″, with optionally the control of the first permeateportion 50′ and second permeate portion 50″ being based on a measurementthe total flow rate of permeate stream 50 in relation to the combinedflow rate of bleed stream 40 and permeate stream 50. In any of thecontrol schemes described above, control may be performed manually orautomatically, for example using a feedback control loop to adjust flowrates, i.e., partitioning, of first permeate portion 50′ and/or secondpermeate portion 50″ on the basis of one or more measured flow rates.]

High and low pressure separators 60, 70 may be used to purify metaboliteproducts (e.g., ethanol) from bleed and permeate streams 40, 50 on thebasis of differences in relative volatility. In the case of thepurification of ethanol, this metabolite may be relatively more volatilethan water and other metabolites such as acetic acid and 2,3-butanediol,as described above. Consequently, ethanol may be enriched (i.e., presentat a higher concentration) in an overhead vapor, withdrawn from highand/or low pressure separator 60, 70, compared to the ethanolconcentration in permeate stream 50, fed to high pressure separator 60,and/or bleed stream 40, fed to low pressure separator 70. Likewise,ethanol may be depleted (i.e., present at a lower concentration) in thebottoms liquid, withdrawn from high and/or low pressure separator 60,70, compared to the ethanol concentration in permeate stream 50, fed tohigh pressure separator 60 and/or bleed stream 40, fed to low pressureseparator 70. High and low pressure separators 60, 70 include flashdrums that perform a separation based on substantially a singletheoretical vapor-liquid equilibrium stage. Preferably, however, highand low pressure separators 60, 70 are distillation columns that performa separation based on multiple theoretical vapor-liquid equilibriumstages, optionally using heat input and output (e.g., reboiler heatinput and condenser heat output), overhead vapor and bottoms liquidreflux, and internal structures such as perforated plates and/or packingmaterials. High and low pressure separators 60, 70, in addition toperforming separations based on multiple vapor-liquid equilibriumstages, may, according to some embodiments, operate with the input of anupwardly flowing auxiliary gas stream (as in the case of a strippingcolumn) or alternatively with the input of a downwardly flowingauxiliary liquid stream (as in the case of an absorber column).

First permeate portion 50′ may be processed in high pressure separator60 (e.g., a high pressure permeate distillation column), to separate, orfractionate, first permeate portion 50′ into at least high pressureseparator overhead 68 and high pressure separator bottoms 52, wherebyhigh pressure separator overhead 68 is enriched in ethanol and highpressure separator bottoms 52 is depleted in ethanol, relative topermeate stream 50. Both high pressure separator overhead 68 and highpressure separator bottoms 52 may therefore be withdrawn from highpressure separator 60. High pressure separator bottoms 52 may becombined with low pressure separator permeate bottoms 66, according tothe embodiment of FIG. 3, as both of these streams are enriched inwater, relative to permeate stream 50. Net permeate bottoms 54 may berecycled to bioreactor system 100 (e.g., by being used in thepreparation of culture medium) or sent to a wastewater treatmentprocess. Likewise, ethanol may be depleted (i.e., present at a lowerconcentration) in the bottoms liquid, withdrawn from high and/or lowpressure separator 60, 70, compared to the ethanol concentration inpermeate stream 50, to high pressure separator 60 and/or bleed stream 40to low pressure separator 70.

As illustrated in the embodiment of FIG. 3, both high pressure separator60 (e.g., high pressure distillation column) and low pressure separator70 (e.g., low pressure distillation column) generally include anoverhead condenser and a bottoms reboiler. In the case of low pressureseparator 70 having divider 80 disposed therein as described above withreference to FIGS. 2 and 3, a low pressure separator bleed reboiler 45may be separate from a low pressure separator permeate reboiler 55.Alternatively, a single low pressure separator reboiler may be used.These low pressure separator reboilers 45, 55 or a combined reboiler, inconjunction with a low pressure separator condenser 65, provide sites ofheat consumption in such reboilers and sites of heat generation in suchcondensers. As illustrated in FIG. 3, high pressure separator condenser75 also provides a site of heat generation, and a high pressureseparator reboiler 85 also provide site of heat consumption. In view ofthe differences in operating temperatures between the high pressureseparator 60 and low pressure separator 70, heat may be transferredbetween these separators, for example by using suitable heat transfermedia such as cooling water or steam to provide the necessary cooling orheating duty, respectively, of the condensers and reboilers, resultingin advantageous heat integration that can reduce operating costs.

As illustrated in FIGS. 2 and 3, one or more of the following may bepossible, in view of the use of overhead condensers and bottomsreboilers: (i) low pressure separator overhead 62, in addition to lowpressure separator overhead reflux portion 63, may be separated from lowpressure separator vapor outlet stream 67 withdrawn from low pressureseparator 70, (ii) low pressure separator bleed bottoms 64, in additionto low pressure separator bleed liquid reflux portion 69, may beseparated from low pressure separator bleed liquid outlet stream 71withdrawn from low pressure separator 70, (iii) low pressure separatorpermeate bottoms 66, in addition to low pressure separator permeateliquid reflux portion 73, may be separated from low pressure separatorpermeate liquid outlet stream 77 withdrawn from low pressure separator70. Further arising from the use of overhead condensers and bottomsreboilers, one or more of the following, particular flow schemes mayalso be possible: (i) low pressure separator vapor outlet stream 67 maybe fed to low pressure separator condenser 65 to condense at least aportion thereof, return low pressure separator overhead reflux portion63 to low pressure separator 70, and recover low pressure separatorcondenser heat 89, (ii) low pressure separator bleed liquid outletstream 71 may be fed to low pressure separator bleed reboiler 45 tovaporize at least a portion thereof, return low pressure separator bleedliquid reflux portion 69 to low pressure separator 70, and consume lowpressure separator bleed reboiler heat 96, (iii) low pressure separatorpermeate liquid outlet stream 77 may be fed to low pressure separatorpermeate reboiler 55 to vaporize at least a portion thereof, return lowpressure separator permeate liquid reflux portion 73 to low pressureseparator 70, and consume low pressure separator permeate reboiler heat97.

Additionally, as illustrated in FIG. 3. (i) high pressure separatoroverhead 68, in addition to high pressure separator overhead refluxportion 79, may be separated from high pressure separator vapor outletstream 81 withdrawn from high pressure separator 60, and (ii) highpressure separator bottoms 52, in addition to high pressure separatorliquid reflux portion 83, may be separated from high pressure separatorliquid outlet stream 87 withdrawn from high pressure separator 60.Further arising from the use of overhead condensers and bottomsreboilers, one or more of the following, particular flow schemes mayalso be possible: (i) high pressure separator vapor outlet stream 81 maybe fed to high pressure separator condenser 75 to condense at least aportion thereof, return high pressure separator overhead reflux portion79 to high pressure separator 60, and recover high pressure separatorcondenser heat 98, and (ii) high pressure separator liquid outlet stream87 may be fed to high pressure separator reboiler 85 to vaporize atleast a portion thereof, return high pressure separator liquid refluxportion 83 to high pressure separator 70, and consume high pressureseparator reboiler heat 99.

Particularly advantageous heat integration strategies involve thetransfer of heat from the high pressure separator to the low pressureseparator, and especially from high pressure separator condenser 75 to areboiler of low pressure separator 70 in the case in which thetemperature of the former exceeds the temperature of latter.Accordingly, at least a portion of high pressure separator condenserheat 98 may be consumed as low pressure separator permeate reboiler heat96 or as low pressure separator bleed reboiler heat 97. In the case of asingle low pressure separator reboiler being used, to which low pressureseparator bleed liquid outlet stream 71 and low pressure separatorpermeate liquid outlet stream 77 are fed to vaporize portions thereof,to return low pressure separator bleed liquid reflux portion 69 and lowpressure separator permeate liquid reflux portion 73 to low pressureseparator 70, and to consume low pressure separator reboiler heat, thenat least a portion of high pressure separator condenser heat 98 may beconsumed as heat for the low pressure separator reboiler.

According to the embodiment of FIG. 3, ethanol contained in both lowpressure separator overhead 62 and high pressure separator overhead 68may represent a net amount of ethanol recovered from bioreactor system100, and consequently a net ethanol productivity of this system. Asdescribed above, bioreactor systems according to the present inventioncan provide advantages in terms of process heat integration,particularly in the face of relatively high permeate stream flow rates,compared to bleed stream flow rates, accompanying high ethanolproductivities. Exemplary ethanol productivities are generally at leastabout 35 grams per day per liter of bioreactor volume (g/day/L), forexample in the range from about 35 g/day/L to about 80 g/day/L,typically at least about 45 g/day/L, for example in the range from about45 g/day/L to about 75 g/day/L, and often at least about 55 g/day/L, forexample in the range from about 55 g/day/L to about 70 g/day/L. Indetermining the productivity rate on the basis of the bioreactor volume,this volume includes continuous liquid phase zones 18, 18′ andcontinuous gas phase zones 22, 22′ of the bioreactor(s) used in thebioreactor system.

Both low pressure separator overhead 62 and high pressure separatoroverhead 68, which are enriched in ethanol, may be combined intodehydration column feed stream 72. Dehydration column fractionates thisstream into anhydrous ethanol product stream 76, comprisingsubstantially pure ethanol (e.g., having a purity of at least about 99%by weight) and residual water stream 74.

According to further embodiments, both low pressure separator bleedbottoms 64 (e.g., comprising, or consisting essentially of, a liquidfraction of bleed stream 40) and low pressure separator permeate bottoms66 (e.g., comprising, or consisting essentially of, a liquid fraction ofsecond permeate portion 50″) may be withdrawn from low pressureseparator 70. Low pressure separator bleed bottoms 64 may be passed toproduct separation system 90, which may be a product membrane filtrationsystem, for the separation and removal of bleed stream biomass fraction78 (e.g., as a retentate fraction obtained from product separationsystem 90) from bleed stream liquid fraction 88 (e.g., as a permeatefraction obtained from product separation system 90). Bleed streamliquid fraction may be re-used in bioreactor system 100 (e.g., followingone or more treatment steps to obtain water suitable for use in thesystem), or alternatively sent to a wastewater treatment facility. Atleast a portion of high pressure separator bottoms 52 and/or at least aportion of low pressure separator permeate bottoms 66, as substantiallypure water streams that optionally comprise higher-boiling metabolitessuch as acetic acid and 2,3-butanediol, may be recycled to bioreactorprocess 100, optionally following one or more treatment steps. Accordingto the embodiment of FIG. 2, these streams 52, 66 may be combined intonet permeate bottoms 54, prior to such recycling and/or treatment. Waterin streams 52, 66 may be recycled, for example, for the preparation offresh culture medium.

In terms of biological conversion apparatuses corresponding to theembodiments depicted in FIGS. 1-3, it is apparent in view of the abovedescription that such apparatuses may comprise a bioreactor system 100comprising (i) an inlet 12 for introducing a CO-containing substrate tothe bioreactor system 100, (ii) at least a first bioreactor 10 forcontaining a culture medium and C1-fixing bacteria to metabolize CO inthe CO-containing substrate and produce ethanol, (iii) a filtrationsystem 25′ for filtering a liquid product of the bioreactor system, (iv)a bleed stream outlet 40 for withdrawing a bleed stream comprisingC1-fixing bacteria, and (v) a permeate stream outlet 50 in fluidcommunication with a permeate side of the filtration system 25′ forwithdrawing a permeate stream from the bioreactor system 100, andoptionally a recycle conduit 36′ in fluid communication with a retentateside of the filtration system 25′ for maintaining a recycle portion ofC1-fixing bacteria in the bioreactor system 100; and a low pressureseparator 70 having a divider 80 disposed in a lower section A thereofand configured for isolating (i) a first liquid volume 82 in fluidcommunication with both (I) the bleed stream outlet 40, at a lowpressure separator bleed stream inlet 91 positioned in the lower sectionA and (II) a low pressure separator bleed bottoms outlet 64 positionedbelow the low pressure bleed stream inlet 91 from (ii) a second liquidvolume 84 in fluid communication with both (I) the permeate streamoutlet 50, at a low pressure separator permeate stream inlet 92positioned in the lower section A and (II) a low pressure separatorpermeate bottoms outlet 66 positioned below the low pressure separatorpermeate stream inlet 92.

The low pressure separator 70 may be configured for combining, in anupper section B thereof, a first gaseous fraction above the first liquidvolume 82 with a second gaseous fraction above the second liquid volume84 and to provide a combined gaseous volume 86 in fluid communicationwith a low pressure separator overhead outlet 62.

The apparatus may optionally further comprise a high pressure separator60 having (i) a first permeate portion inlet 93 in fluid communicationwith the permeate stream outlet 50, for receiving a first permeateportion of the permeate stream and passing a second permeate portion ofthe permeate stream to the low pressure separator permeate stream inlet92, (ii) a high pressure separator overhead outlet 68, and (iii) a highpressure separator bottoms outlet 52, wherein the first permeate portioninlet 93 is positioned below the high pressure separator overhead outlet68 and above the high pressure separator bottoms outlet 52.

Low pressure separator 70 may be configured with low pressure separatorcondenser 65 in fluid communication with low pressure separator vaporoutlet 67 and both (i) low pressure separator overhead reflux conduit 63and (ii) low pressure separator overhead conduit 62. Low pressureseparator may also be configured with low pressure separator bleedreboiler 45 in fluid communication with low pressure separator bleedliquid outlet 71 and both (i) low pressure separator bleed liquid refluxconduit 69 and (ii) low pressure separator bleed bottoms conduit 64. Lowpressure separator 70 may be further configured with low pressureseparator permeate reboiler 55 in fluid communication with low pressureseparator permeate liquid outlet 77 and both (i) low pressure separatorpermeate liquid reflux conduit 73 and low pressure separator permeatebottoms conduit 66. In lieu of being configured with both a low pressureseparator bleed reboiler and a low pressure separator permeate reboiler,as illustrated in FIG. 2, low pressure separator 70 may alternatively beconfigured with a low pressure separator reboiler in fluid communicationwith both low pressure separator bleed liquid outlet 71 and low pressureseparator permeate liquid outlet 77, in addition to low pressureseparator bleed liquid reflux conduit 69 and low pressure separatorpermeate liquid flux conduit 73, as well as low pressure separator bleedbottoms conduit 64 and low pressure separator permeate bottoms conduit66.

High pressure separator 60 may be configured with high pressureseparator condenser 75 in fluid communication with high pressureseparator vapor outlet 81 and both (i) high pressure separator overheadreflux conduit 79 and (ii) high pressure separator overhead conduit 68.High pressure separator 60 may also be configured with high pressureseparator reboiler 85 in fluid communication with high pressureseparator liquid outlet 87 and both (i) high pressure separator liquidreflux conduit 83 and (ii) high pressure separator bottoms conduit 52.Any of, or any combination of, low pressure separator condenser 65, lowpressure separator bleed reboiler 45, low pressure separator permeatereboiler 55, and the low pressure separator reboiler (replacing separatelow pressure reboilers 45, 55), as described above, may be configured toprovide heat integration with high pressure separator condenser 75and/or high pressure separator reboiler 85, as described above.According to exemplary embodiments, high pressure separator condenser 75may be configured (e.g., using a heat transfer medium such as coolingwater or steam) to transfer heat generated in this condenser, forconsumption in low pressure separator bleed reboiler 45 and/or the lowpressure separator permeate reboiler 55, or the low pressure separatorreboiler (replacing separate low pressure reboilers 45, 55), asdescribed above.

The apparatus may optionally further comprise a dehydration column 95having (i) a dehydration column inlet 72 in fluid communication withboth the low pressure separator overhead outlet 62 and the high pressureseparator overhead outlet 68, (ii) a dehydration column overhead outlet76, and (iii) a dehydration column bottoms outlet 74, wherein thedehydration column inlet 72 is positioned below the dehydration columnoverhead outlet 76 and above the dehydration column bottoms outlet 74.

The apparatus may optionally further comprise a product filtrationsystem 90 in fluid communication with the low pressure separator bleedbottoms outlet 64 for filtering a low pressure separator bleed bottomsstream.

Overall, aspects of the disclosure are associated with biologicalconversion processes involving downstream recovery of ethanol from bleedand permeate streams and relate, more particularly, to performing suchrecovery with improved efficiency that can advantageously reduce capital(e.g., equipment) and/or operating (e.g., utility) costs. Those havingskill in the art, with the knowledge gained from the present disclosure,will recognize that various changes could be made to these processes inattaining these and other advantages, without departing from the scopeof the present disclosure. As such, it should be understood that thefeatures of the disclosure are susceptible to modification, alteration,changes, or substitution without departing from the scope of thisdisclosure. The specific embodiments illustrated and described hereinare for illustrative purposes only, and not limiting of the invention asset forth in the appended claims.

1. A biological conversion process comprising: feeding a substrate to abioreactor system comprising at least a first bioreactor including aculture medium and bacterium to metabolize a carbon source in thesubstrate and produce at least one fermentation product; withdrawingfrom the bioreactor system a bleed stream comprising bacteriumwithdrawing from the bioreactor system a permeate stream obtained fromfiltration of a liquid stream of the bioreactor system; feeding at leasta portion of the bleed stream and at least a portion of the permeatestream to a low pressure separator comprising a divider, the dividerbeing configured to isolate, in a lower section, a liquid fraction ofthe bleed stream from a liquid fraction of the permeate stream and alsoconfigured to combine, in an upper section, a gaseous fraction of thebleed stream with a gaseous fraction of the permeate stream.
 2. Theprocess of claim 1 further comprising partitioning the permeate streaminto at least a first permeate portion and a second permeate portion;feeding the first permeate portion-to a high pressure separator andfeeding the second permeate portion to the low pressure separator;withdrawing, from the high pressure separator, a high pressure separatoroverhead and a high pressure separator bottom wherein the high pressureseparator overhead is enriched in desired fermentation product relativeto the first permeate portion; and withdrawing a low pressure separatoroverhead enriched in desired fermentation product, relative to both thesecond permeate portion and the bleed stream.
 3. The process of claim 2wherein the high pressure separator and the low pressure separator are ahigh pressure distillation column and a low pressure distillationcolumn, respectively.
 4. The process of claim 2, wherein the highpressure separator has an absolute pressure in the range from about 150kPa to about 650 kPa.
 5. The process of claim 2, wherein the lowpressure separator has a vacuum pressure.
 6. The process of claim 2,further comprising withdrawing, from the low pressure separator, both alow pressure separator bleed bottoms and a low pressure separatorpermeate bottoms.
 7. The process of claim 2, wherein one or more of (i)the low pressure separator overhead, in addition to a low pressureseparator overhead reflux portion, are separated from a low pressureseparator vapor outlet stream withdrawn from the low pressure separator,(ii) the low pressure separator bleed bottoms, in addition to a lowpressure separator bleed boilup portion, are separated from a lowpressure separator bleed liquid outlet stream withdrawn from the lowpressure separator, (iii) the low pressure separator permeate bottoms,in addition to a low pressure separator permeate boilup portion, areseparated from a low pressure separator permeate liquid outlet streamwithdrawn from the low pressure separator, (iv) the high pressureseparator overhead, in addition to a high pressure separator overheadreflux portion, are separated from a high pressure separator vaporoutlet stream withdrawn from the high pressure separator, and (v) thehigh pressure separator bottoms, in addition to a high pressureseparator boilup portion, are separated from a high pressure separatorliquid outlet stream withdrawn from the high pressure separator.
 8. Theprocess of claim 7, wherein one or more of (i) the low pressureseparator vapor outlet stream is fed to a low pressure separatorcondenser to condense at least a portion thereof, return the lowpressure separator overhead reflux portion to the low pressureseparator, and recover low pressure separator condenser heat, (ii) thelow pressure separator bleed liquid outlet stream is fed to a lowpressure separator bleed reboiler to vaporize at least a portionthereof, return the low pressure separator bleed boilup portion to thelow pressure separator, and consume low pressure separator bleedreboiler heat, (iii) the low pressure separator permeate liquid outletstream is fed to a low pressure separator permeate reboiler to vaporizeat least a portion thereof, return the low pressure separator permeateboilup portion to the low pressure separator, and consume low pressureseparator permeate reboiler heat, (iv) the high pressure separator vaporoutlet stream is fed to a high pressure separator condenser to condenseat least a portion thereof, return the high pressure separator overheadreflux portion to the high pressure separator, and recover high pressureseparator condenser heat, and (v) the high pressure separator liquidoutlet stream is fed to a high pressure separator reboiler to vaporizeat least a portion thereof, return the high pressure separator boilupportion to the high pressure separator, and consume high pressureseparator reboiler heat.
 9. The process of claim 8, wherein at least aportion of the high pressure separator condenser heat is consumed as lowpressure separator permeate reboiler heat or as low pressure separatorbleed reboiler heat.
 10. The process of claim 7, wherein the lowpressure separator bleed liquid outlet stream and the low pressureseparator permeate liquid outlet stream are fed to a low pressureseparator reboiler to vaporize portions thereof, return the low pressureseparator bleed liquid reflux portion and the low pressure separatorpermeate liquid reflux portion to the low pressure separator, andconsume low pressure separator reboiler heat.
 11. The process of claim10, wherein at least a portion of the high pressure separator condenserheat is consumed as low pressure separator reboiler heat.
 12. Theprocess of claim 2, wherein the divider is in the form of a verticallyoriented plate, extending to a height that is less than an axial heightof the low pressure separator.
 13. The process of claim 2, wherein theliquid fraction of the bleed stream provides a first liquid volume influid communication with the low pressure separator bleed bottoms andthe liquid fraction of the second permeate portion provides a secondliquid volume in fluid communication with the low pressure separatorpermeate bottoms, and wherein the first volume is smaller than thesecond volume.
 14. The process of claim 2, further comprising recyclingat least a portion of the high pressure separator bottoms and at least aportion of the low pressure separator permeate bottoms to the bioreactorsystem.
 15. The process of claim 1, wherein the substrate is aC1-containing substrate, the bacterium is a C1-fixing bacterium, and theat least one fermentation product is selected from the group consistingof ethanol, isopropanol and mixtures thereof.
 16. The process of claim15, wherein the process does not include an additional separator forfractionating an additional permeate stream.
 17. A biological conversionapparatus comprising: a bioreactor system comprising (i) an inlet forintroducing a substrate to the bioreactor system, (ii) at least a firstbioreactor for containing a culture medium and bacterium to metabolize acarbon source in the substrate and produce a product, (iii) a filtrationsystem for filtering a liquid product of the bioreactor system, (iv) ableed stream outlet for withdrawing a bleed stream comprising bacterium,and (v) a permeate stream outlet in fluid communication with a permeateside of the filtration system for withdrawing a permeate stream from thebioreactor system; and a low pressure separator having a dividerdisposed in a lower section thereof and configured for isolating (i) afirst liquid volume in fluid communication with both (A) the bleedstream outlet, at a low pressure separator bleed stream inlet positionedin the lower section and (B) a low pressure separator bleed bottomsoutlet positioned below the low pressure bleed stream inlet from (ii) asecond liquid volume in fluid communication with both (A) the permeatestream outlet, at a low pressure separator permeate stream inletpositioned in the lower section and (B) a low pressure separatorpermeate bottoms outlet positioned below the low pressure separatorpermeate stream inlet; wherein the low pressure separator is configuredfor combining, in an upper section thereof, a first gaseous fractionabove the first liquid volume with a second gaseous fraction above thesecond liquid volume and to provide a combined gaseous volume in fluidcommunication with a low pressure separator overhead outlet, theapparatus optionally further comprising a high pressure separator having(i) a first permeate portion inlet in fluid communication with thepermeate stream outlet, for receiving a first permeate portion of thepermeate stream and passing a second permeate portion of the permeatestream to the low pressure separator permeate stream inlet, (ii) a highpressure separator overhead outlet, and (iii) a high pressure separatorbottoms outlet, wherein the first permeate portion inlet is positionedbelow the high pressure separator overhead outlet and above the highpressure separator bottoms outlet; the apparatus optionally furthercomprising a dehydration column having (i) a dehydration column inlet influid communication with both the low pressure separator overhead outletand the high pressure separator overhead outlet, (ii) a dehydrationcolumn overhead outlet, and (iii) a dehydration column bottoms outlet,wherein the dehydration column inlet is positioned below the dehydrationcolumn overhead outlet and above the dehydration column bottoms outlet;and the apparatus optionally further comprising a second filtrationsystem in fluid communication with the low pressure separator bleedbottoms outlet for filtering a low pressure separator bleed bottomsstream.